I. Field of the Invention
This invention relates generally to implantable tissue stimulating apparatus of the type having a pulse generator and a medical lead for delivering electrical stimulation to target tissue, and more particularly to a tool to be used in facilitating the surgical implantation of a medical lead into a patient's body.
II. Discussion of the Prior Art
In implanting medical devices, such as pacemakers or pacemakers/defibrillators, a transvenous lead placement approach has found wide acceptance. Using the Seldinger technique, the right or left cephalic vein or the axillary vein is located and punctured with a relatively long, large-bore needle. A guidewire is then typically passed through the needle into the selected vein. The needle is then removed from the guidewire and replaced with an introducer incorporating a hemostasis valve to stem blood flow. Once the introducer is in place, the medical lead is forced through the hemostasis valve, the introducer's shaft, and thence, through the selected vein and ultimately into a selected chamber of the heart.
An introducer that has found rather wide spread acceptance is the SafeSheath® manufactured and sold by Pressure Products of Rancho Palo Verdes, Calif. It incorporates a tear-away sheath having a break-away hemostasis valve assembly affixed to a proximal end of the sheath. The hemostasis valve assembly comprises a molded plastic housing containing an elastomeric disk having a self-closing aperture formed through its thickness dimension. The SafeSheath also includes a side entry port located distally of the housing containing the hemostasis valve whereby fluids containing an anti-coagulant may be infused through the lumen of the sheath and into the selected vein.
Once the introducer is installed, a medical lead having one or more electrode surfaces at its distal end is passed through the hemostasis valve of the introducer and thence, through its sheath until the electrodes are positioned at a desired site within the heart. Once the distal end of the lead is appropriately placed, the introducer may be removed from the lead by splitting the break-away hemostasis valve assembly and the sheath.
While introducers of the type described can be used with a variety of pacemaker/defibrillator leads, there are certain lead designs that can be damaged as the distal end portion bearing the electrodes is forced through the self-closing aperture of the hemostatic valve. The shocking electrodes on defibrillator leads are often in the form of an uninsulated wire coil supported by the lead's plastic body. As a lead of this type is forced through the hemostasis valve of an introducer, the excessive frictional forces tend to displace the turns of the coil so that they are no longer appropriately spaced.
Other leads with which the SafeSheath introducer is incompatible are those in which a fabric covering is placed over the coil electrodes of defibrillator leads to inhibit tissue ingrowth into the coils of the shocking electrode. Because of the porosity of the fabric, electrical shocking currents readily pass through to surrounding tissue with very low impedance. However, it is found that the SafeSheath introducer incorporates a silicon oil as a lubricant on its hemostasis valve member and as such a fabric covered electrode of the lead is forced through the self-closing aperture, the silicon oil wipes off onto the fabric covering that tends to plug the pores in the fabric which adversely impacts the lead's electrical performance. Then, too, when attempting to pass this lead through the valve, frictional forces tend to displace the fabric covering, in effect, peeling it back. Another drawback of the hemostatic valve's direct engagement with the medical lead being implanted is that tactile feedback through the lead to the physician's fingers is severely dampened.
From the foregoing discussion, those skilled in the art will appreciate that a need exists for a lead insertion tool that will obviate the cited drawbacks of state-of-the-art lead introducers incorporating a hemostasis valve. The present invention provides such a device.